Title: PowerLecture: Chapter 14
1PowerLectureChapter 14
2Learning Objectives
- Describe the characteristics of a receptor and
list the various types of receptors. - Contrast mechanisms by which the chemical and the
somatic senses work. - Understand how the senses of balance and hearing
function. - Describe how the sense of vision has evolved
through time.
3Learning Objectives (contd)
- Draw a medial section of the human eyeball
through the optic nerve, identify each structure,
and tell the function of each. - Identify some common disorders of the eye.
4Impacts/Issues
5Private Eyes
- Iris scanning is one of the newest
- security techniques.
- First, each persons unique
- arrangement of smooth muscle fibers in
- the iris of the eye must be recorded in
- an electronic database.
- Each time the person passes through
- a check point, a small camera looks at the iris
and compares it with the database. - Usually, we use our eyes to see, but in this new
technology, our eyes are seen.
6How Would You Vote?
- To conduct an instant in-class survey using a
classroom response system, access JoinIn Clicker
Content from the PowerLecture main menu. - In which situations should individuals be
required to submit to iris scanning and
registration? - a. For any reason it's not any different than
other forms of identification. - b. In place of or to enhance government
identification, such as a driver's license or
passport. - c. For employment at any company that chooses to
require it. - d. It should never be required, it should only be
used as a voluntary convenience, and then,
strictly regulated.
7Section 1
- Sensory Receptors and Pathways
8Sensory Receptors and Pathways
- In a sensory system, a stimulus activates a
receptor, which transduces (converts) it to an
action potential that travels to the brain where
it triggers sensation or perception. - A stimulus is any form of energy that activates
receptor endings of a sensory neuron. - Sensations are conscious responses to the
stimuli. - Perception is an understanding of what sensations
mean.
9In-text Fig., p. 250
stimulus energy received
stimulus energy converted to action potential
brain response (sensation or perception)
10Fig. 14.1, p. 251
Stretched muscle stimulates a stretch receptor
(the ending of a sensory neuron) that is adjacent
to it.
c
d
Message travels from stimulated sensory neuron to
motor neuron and interneuron in spinal cord.
sensory neuron
interneuron in spinal cord
motor neuron in spinal cord
e
Message is sent back to the muscle, also to
other interneurons in the brain.
axon endings of motor neuron terminating on the
same muscle
muscle spindle
b
11Sensory Receptors and Pathways
- Six major categories of sensory receptors.
- Mechanoreceptors detect changes in pressure,
position, or acceleration. - Thermoreceptors detect heat or cold.
- Nociceptors (pain receptors) detect tissue
damage. - Chemoreceptors detect ions or molecules.
- Osmoreceptors detect changes in solute
concentration in surrounding fluid. - Photoreceptors detect the energy of visible
light.
12Animation Mechanoreceptors
CLICKTO PLAY
13(No Transcript)
14Sensory Receptors and Pathways
- All action potentials are the same the brain
determines the nature of a given stimulus based
on which nerves are signaling, the frequency of
the action potentials generated, and the number
of axons responding. - Specific sensory areas interpret action
potentials in specific ways. - Strong signals make receptors fire action
potentials more often and longer.
15Sensory Receptors and Pathways
- Stronger stimuli recruit more sensory receptors.
- Sensory adaptation is the diminishing response to
an ongoing stimulus.
Figure 14.1
16Section 2
17Somatic Sensations
- Somatic sensations occur when receptor signals
from body surfaces reach the somatosensory cortex
in the cerebrum.
Figure 14.3
18Animation Somatosensory Cortex
CLICKTO PLAY
19Somatic Sensations
- Receptors near the body surface sense touch,
pressure, and more. - Sensations of touch, pressure, cold, warmth, and
pain are discerned near the body surface by
receptors whose numbers vary by body region. - Free nerve endings are the simplest receptors.
- These are thinly myelinated or unmyelinated
dendrites of sensory neurons. - One type coils around hair follicles to detect
movement another detects chemicals.
20Somatic Sensations
- Encapsulated receptors are surrounded by a
capsule of epithelial or connective tissue. - Merkels discs adapt slowly and
- are important for steady touch.
- Meissners corpuscles respond
- to light touching.
- Ruffini endings are sensitive to
- steady touch and pressure.
- The Pacinian corpuscles are
- sensitive to deep pressure and
- vibrations.
Figure 14.4
21Animation Sensory Receptors
CLICKTO PLAY
22Fig. 14.4, p. 253
free nerve endings (pain)
Meissners corpuscle (light touch)
hair
Meissners corpuscle
epidermis
Merkels discs (steady touch)
Ruffini endings (pressure, touch)
dermis
Merkels discs
subcutaneous layer
Pacinian corpuscle (deep pressure, vibrations)
hair follicle receptor (hair displacement)
Ruffini endings
Pacinian corpuscle
23Somatic Sensations
- Mechanoreceptors in skeletal muscle, joints,
tendons, ligaments, and skin are responsible for
awareness of the bodys position and of its limb
movements. - Pain is the perception of bodily injury.
- Pain is the perception of injury to some region
of the body.
24Somatic Sensations
- Nociceptors are subpopulations of free nerve
endings distributed throughout the skin (somatic
pain) and internal tissues (visceral pain). - When cells are damaged, they release chemicals
(bradykinins, histamine, and prostaglandins) to
activate neighboring pain receptors. - Pain receptors signal interneurons, which release
substance P. - Substance P allows for natural opiates called
endorphins and enkephalins to be released to
reduce pain perception.
25Somatic Sensations
- Referred pain is a matter of perception.
- Much visceral pain is referred pain that is,
- it is felt at some distance from the real
stimulation point. - Phantom pain is the sensation that amputees feel
when they sense the missing part as if it were
still there.
26Fig. 14.5, p. 253
lungs,diaphragm
heart
stomach
liver, gallbladder
pancreas
small intestine
ovaries
colon
appendix
urinary bladder
kidney
ureter
27Animation Referred Pain
CLICKTO PLAY
28Section 3
- Taste and Smell
- Chemical Senses
29Taste and Smell Chemical Senses
- Taste and smell are chemical senses they begin
at chemoreceptors, the signals traveling to the
brain where they are perceived, transmitted to
the limbic system, and remembered.
30Taste and Smell Chemical Senses
- Gustation is the sense of taste.
- Sensory organs called taste buds hold the taste
receptors. - Receptors are located on the tongue, roof of the
mouth, and throat. - The five general taste categories are sweet,
sour, salty, bitter, and umami. - The flavors of most foods are a combination of
the five basic tastes plus sensory input from
olfactory receptors in the nose.
31Animation Taste Receptors
CLICKTO PLAY
32Fig. 14.6, p. 254
a
taste bud
tonsil
hairlike ending of taste receptor
bitter
sour
salty
sweet
c
sensory nerve
d
b
33Taste and Smell Chemical Senses
- Olfaction is the sense of smell.
- Olfactory receptors in the olfactory epithelium
of the nose detect water-soluble or volatile
substancesodors. - The interpretation of smell is done by the
olfactory bulbs located in the brain. - Olfaction is one of the most ancient senses,
useful in survival as the receptors respond to
molecules from food, mates, and predators. - Humans also have a vomeronasal organ whose
receptors can detect pheromones, which are
signaling molecules with roles in sexual
attraction.
34Animation Olfactory Pathway
CLICKTO PLAY
35Fig. 14.7, p. 255
olfactory nerve tract
olfactory bulb
olfactory receptor cell body
36Video Tongue Tied
CLICKTO PLAY
- From ABC News, Human Biology in the Headlines,
2006 DVD.
37Section 4
- A Tasty Morsel of Sensory Science
38A Tasty Morsel of Sensory Science
- Receptors in taste buds associate the five main
taste categories with particular tastant
molecules that the brain interprets depending on
the action potentials that come its way. - Each taste bud has receptors that can respond to
tastants of at least two, if not all five, of the
taste classes. - Not all taste receptors, however, are equally
sensitive bitter receptors tend to be the most
sensitive.
39A Tasty Morsel of Sensory Science
- Various tastants commingle together with odors
into what we perceive as flavors.
40Section 5
- Hearing Detecting Sound Waves
41Hearing Detecting Sound Waves
- Sounds are waves of compressed air the amplitude
(loudness) and frequency (pitch) of sounds are
detected by vibration-sensitive mechanoreceptors
deep in the ear.
one cycle
Low note
Soft
Amplitude
High note
Loud
Same loudness, different pitch
Same frequency, different amplitude
Frequency per unit time
Figure 14.8
42Animation Wavelike Properties of Sound
CLICKTO PLAY
43Hearing Detecting Sound Waves
- The ear gathers and sends sound signals to the
brain. - The outer ear collects sound waves and turns them
into vibrations, which are amplified in the
middle ear vibrations are distinguished in the - inner ear.
- Inner ear structures include semicircular canals
for balance and the cochlea where hearing takes
place.
44Hearing Detecting Sound Waves
- Sensory hair cells are the key to hearing.
- Vibrations are passed from the tympanic membrane
to the middle ear bones (malleus, incus, stapes)
and on to the oval window, stretched across the
entrance to the cochlea. - Sound is amplified because the oval window is
smaller than the tympanic membrane. - The cochlea has two compartments in its outer
chamber (the scala vestibuli and scala tympani),
which curl around an inner cochlear duct all are
fluid filled.
45Fig. 14.9a, p. 256
46Fig. 14.9a, p. 256
INNER EAR vestibular apparatus, cochlea
MIDDLE EAR eardrum, ear bones
OUTER EAR pinna, auditory canal
47Fig. 14.9b, p. 256
OVAL WINDOW (behind stirrup)
MIDDLE EAR BONES
stirrup
auditory nerve
anvil
hammer
COCHLEA
round window
auditory canal
EARDRUM
48Fig. 14.9c, p. 257
oval window (behind stirrup)
waves of air pressure
waves of fluid pressure
scala vestibuli
eardrum
scala tympani
cochlear duct
round window
49Hearing Detecting Sound Waves
- Vibrations of the oval window send pressure waves
through the fluid to the basilar membrane on the
floor of the cochlear duct resting on the
membrane is the organ of Corti, which includes
sensory hair cells. - The tips of the hair cells rest against the
jellylike tectorial membrane vibrations cause
the hair cells to bend. - Bending causes the release of neurotransmitters,
triggering action potentials that travel to the
brain.
50scala vestibuli
cochlear duct
organ of Corti
scala tympani
sensory neurons (to the auditory nerve)
Fig. 14.9d, p. 257
51Hearing Detecting Sound Waves
- Loudness is determined by the total number of
cells that become stimulated tone or pitch
depends on the frequency of vibration. - The round window at the far end of the cochlea
serves as a release valve for the pressure waves
in the middle ear. - The eustachian tube extending from the middle ear
to the throat permits equalization of pressures.
52Animation Ear Structure and Function
CLICKTO PLAY
53Video Sound Detection
CLICKTO PLAY
54Section 6
- Balance Sensing the Bodys Natural Position
55Balance Sensing the Bodys Natural Position
- The sense of balance depends on messages from
receptors in the eyes, skin, and joints, as well
as organs of equilibrium in the inner ear. - The vestibular apparatus is a closed system of
fluid-filled sacs and semicircular canals inside
the ear the canals are arranged to represent the
three planes of space.
Figure 14.10
56Animation Vestibular Apparatus and Equilibrium
CLICKTO PLAY
57Balance Sensing the Bodys Natural Position
- Rotational receptors are located at the base of
each semicircular canal sensory hair cells
project into a jellylike cupula. - Movement of the head causes the hairs to bend
within the jelly, generating action potentials. - Rotation of the head determines dynamic
equilibrium.
58Animation Dynamic Equilibrium
CLICKTO PLAY
59Balance Sensing the Bodys Natural Position
- Static equilibrium, the heads position in space,
is monitored by two sacs in the vestibular
apparatus, the utricle and saccule. - The sacs contain the otolith organs (hair cells)
and otoliths (ear stones), which detect changes
in orientation as well as acceleration and
deceleration. - Action potentials from different parts of the
vestibular apparatus travel to reflex centers in
the brainstem. - As signals are integrated, the brain orders
compensatory movements necessary to maintain
postural balance.
60Fig. 14.10, p. 258
vestibular apparatus, a system of fluid-filled
sacs and canals inside the ear
A vestibular apparatus (part of each inner ear)
consists of a utricle, a saccule, and the three
canals labeled here.
superior canal
posterior canal
utricle
horizontal canal
saccule
nerve
fluid pressure
61stereocilium
otolith
cupula
hair cell
sensory neuron
Fig. 14.11, p. 258
62Balance Sensing the Bodys Natural Position
- Extreme motion or continuous overstimulation of
the hair cells of the vestibular apparatus can
result in motion sickness.
63Section 7
64Disorders of the Ear
- The hearing apparatus of the ears is sturdy, but
it can be damaged by various illnesses and
injuries. - Otitis media, painful inflammation of the middle
ear, often occurs in children following spread of
a respiratory infection pus and/or fluid buildup
as a result can cause the eardrum to rupture. - Tinnitus, or ringing or buzzing in the ears, can
be triggered by infection, aspirin consumption,
or other, unknown causes.
65Disorders of the Ear
- Deafness is the partial or complete loss of
hearing deafness may be congenital or due to
aging, disease, or environmental causation. - The loudness of sounds is measured in decibels.
- Quiet conversation occurs at about 50 decibels.
- Damage begins when exposed to sounds
- between 75-85 decibels over extended periods.
- Rock concerts easily reach 130 decibels.
66Outer Hair Cells
scars
Fig. 14.13, p. 259
67Section 8
68Vision An Overview
- Vision is an awareness of the position, shape,
brightness, distance, and movement of visual
stimuli as detected by the sensory organs, the
eyes. - The eye is built for photoreception.
- The eye has three layers, sometimes called
tunics. - The outer layer consists of the sclera and
transparent cornea. - The middle layer consists of a choroid, ciliary
body, and iris. - The inner layer is the retina.
69Vision An Overview
- The sclera (white of the eye) protects the eye
the dark-pigmented choroid underlies the sclera
and prevents light from scattering. Most of the
blood vessels lie in the choroid. - Behind the cornea is the pigmented iris the hole
at the center of the iris is the pupil, the
entrance for light which can be adjusted
depending on the level of light present. - The lens is found behind the iris the lens is
attached to the ciliary body, a muscle
functioning in the focusing of light. - The lens focuses light onto a layer of
photoreceptor cells in the retina.
70Vision An Overview
- A clear fluid (aqueous humor) bathes both sides
of the lens vitreous humor fills the chamber
behind the lens. - The retina is a thin layer of neural tissue at
the back of the eyeball axons from some of the
neurons converge to form the optic nerve, which
sends signals to the visual cortex in the
thalamus.
71Animation Eye Structure
CLICKTO PLAY
72Parts of the Eye
73Vision An Overview
- The curved surface of the cornea bends incoming
light so that light rays converge at the back of
the eyeball images appear upside down and
backwards on the retina but are corrected in the
brain. - Eye muscle movements fine-tune the focus.
- Because of the bending of the light rays by the
cornea, accommodation must be made by the lens so
that the image is in focus on the retina. - Accommodation is performed by the ciliary muscles
attached to the lens.
74Vision An Overview
- Eye muscle movements fine-tune the focus.
- Because of the bending of the light rays by the
cornea, accommodation must be made by the lens so
that the image is in focus on the retina. - Accommodation is performed by the ciliary muscles
attached to the lens.
75Fig. 14.15a, p. 261
76Fig. 14.16, p. 261
muscle contracted
close object
slack fibers
Accommodation for close objects (lens bulges)
muscle relaxed
distant object
taut fibers
Accommodation for distant objects (lens flattens)
77Animation Visual Accomodation
CLICKTO PLAY
78Video To See Again
CLICKTO PLAY
- From ABC News, Biology in the Headlines, 2005 DVD.
79Section 9
- From Visual Signals
- to Sight
80From Visual Signals to Sight
- Rods and cones are the photoreceptors.
- The retinas basement layer is pigmented and is
covered by photoreceptors called rod cells and
cone cells. - Rod cells are sensitive to dim light and detect
changes in light intensity cone cells respond to
high-intensity light and contribute to sharp
daytime vision.
81Fig. 14.17a, p. 262
82Fig. 14.17b, p. 262
rod cell
stacked, pigmented membranes
cone cell
83From Visual Signals to Sight
- Visual pigments in rods and cones intercept light
energy.
84From Visual Signals to Sight
- Each rod contains more than a billion molecules
of rhodopsin this pigment can detect and respond
to even a few photons of light, allowing us to
see in dim light. - Rhodopsin consists of a protein (opsin) and a
signal molecule (cis-retinal) that is derived
from vitamin A. - Photons of blue-green light stimulate rhodopsin
to change shape shape changes alter the
distribution of ions across the rod cell membrane
and slow down the release of an inhibitory
neurotransmitter. - Without the inhibitor, neurons send visual
signals to the brain.
85From Visual Signals to Sight
- Cone cells have different visual pigments (red,
green, or blue) absorption of photons also
prevents release of neurotransmitters, thus
allowing signaling to the brain. - Visual acuity is
- greatest in the fovea,
- a depression located
- at the center of the
- retina that is densely
- packed with
- photoreceptors.
Figure 14.18
86From Visual Signals to Sight
- The retina processes signals from rods and cones.
- Signals flow from rods and cones to bipolar
interneurons, and then to ganglion cells, the
axons of which form the optic nerves. - Before leaving the retina, signals are dampened
or enhanced by horizontal cells and amacrine
cells.
87Fig. 14.19, p. 263
horizontal cells
amacrine cells
rods
cones
incoming rays of light
ganglion cells (axons get bundled into one of two
optic nerves)
bipolar cells
88Animation Organization of Cells in the Retina
CLICKTO PLAY
89From Visual Signals to Sight
- Receptive fields in the retina.
- The retinas surface is organized into receptive
fields, areas that influence the activity of
individual sensory neurons. - Some fields respond to differences in light,
others to motion, color, or rapid changes in
light intensity. - Signals move on to the visual cortex.
- The visual field represents the part of the
outside world a person actually sees. - The right side of each retina gathers light from
the left half of the visual field and the left
side gathers light from the right half of the
field.
90From Visual Signals to Sight
- The optic nerve from each eye sends signals from
the left visual field to the right cerebral
hemisphere, and signals from the right visual
field to the left hemisphere. - Axons of the optic nerves end in the lateral
geniculate nucleus, from which they proceed to
the brains visual cortex, which has several
visual fields sensitive to direction, movement,
color, and so on here is where final
interpretation of the signals is made to produce
an organized sense of sight.
91Fig. 14.20, p. 263
lateral geniculate nucleus
to optic nerve
optic nerve
visual cortex
retina
92Animation Pathway to the Visual Cortex
CLICKTO PLAY
93Section 10
94Disorders of the Eye
- Normal eye function can be disrupted by disease,
injury, inherited abnormalities, and aging. - Missing cone cells cause color blindness.
- Total color blindness results when an individual
has only one of the three kinds of cones.
95Disorders of the Eye
- Red-green color blindness is the inability to
distinguish red and green colors in dim light
(and sometimes bright light) due to a lack of red
and green cone cells. - Malformed eye parts cause common focusing
problems. - In astigmatism, one or both corneas have uneven
curvature and cannot bend light to the same focal
point.
Figure 14.23
96Disorders of the Eye
- Nearsightedness (myopia) results when the image
is focused in front of the retina. - Farsightedness (hyperopia) is due to an image
focused behind the retina.
Figure 14.21
97Fig. 14.21 (top), p. 264
(focal point)
(focal point)
distant object
close object
98Fig. 14.21 (bottom), p. 264
99Animation Focusing Problems
CLICKTO PLAY
100Disorders of the Eye
- The eyes are also vulnerable to infections and
cancer. - Conjunctivitis, inflammation of the membrane
lining the inside of the eyelids and covering the
sclera, is among the - most common reasons
- for doctor visits in the
- U.S.
Figure 14.22
101Disorders of the Eye
- Trachoma, caused by the bacterium responsible for
the sexually transmitted disease chlamydia,
damages both the eyeball and the conjunctiva,
possibly leading to blindness. - Herpes infection of the cornea results from
infection with various herpes simplex viruses and
can also lead to blindness. - Malignant melanoma is eye cancer that develops in
the choroid retinoblastoma is cancer of the
retina that occurs in infants.
102Disorders of the Eye
- Aging increases the risk of cataracts and some
other eye disorders. - Cataracts, the gradual clouding of the lens
associated with aging and diabetes, can
completely block light from entering the eye. - Macular degeneration is an age-related
degeneration of the retina. - Glaucoma results from excess of fluid in the
eyeball, causing pressure on the retina.
103Disorders of the Eye
- Medical technologies can remedy some vision
problems and treat eye injuries. - Corneal transplant surgery can replace defective
corneas with artificial plastic corneas or donor
corneas cataracts may be corrected in a similar
fashion by replacing the lens. - Lasik (laser-assisted in situ keratomilieusis)
or lasek (laser-assisted subepithelial
keratectomy) surgeries can be used to correct
severe nearsightedness.
104Disorders of the Eye
- Conductive keratoplasty (CK) uses radio waves to
reshape the cornea. - Retinal detachment can result from a physical
blow to the head laser coagulation can be used
to reattach the retina to the underlying
choroid.